ethernet point to point wiring

ethernet point to point wiring

NewsGroups | Search | Tools
 comp.dcom.lans.ethernet  Post an article  get this group's latest topics as an RSS feed add this group's latest topics to your My MSN content add this group's latest topics to your My Yahoo content  add this group's latest topics to your Google content  YahooMyWeb Yahoo!  Google Google  Windows Live Favorites Windows Live  del.icio.us del.icio.us  digg digg  Add to Netscape Netscape
Subject Author Date
ethernet point to point wiring Eddie 10-28-2005
Posted by on October 31, 2005, 8:45 am
If you were  Registered and logged in, you could reply and use other advanced thread options


1. Eddie Oct 28, 8:30 pm show options

Newsgroups: comp.dcom.lans.ethernet
Date: 28 Oct 2005 13:30:35 -0700
Local: Fri, Oct 28 2005 8:30 pm
Subject: ethernet point to point wiring
Reply | Reply to Author | Forward | Print | Individual Message | Show
original | Report Abuse

> I am looking to replace an old serial RS485 multidrop point to point
> communications line with ethernet but would like to retain the wiring
> savings in a point to point layout. On RS485 we can connect 32 devices
> with series point to point wiring. I have done some research that
> indicates that if I used a switch at each device I would be limited to
> a maximum of 7. Is this correct, or are new switches able to exceed
> that number? If so, how many can I realistically connect in a point to
> point topology.

Is I understand it the 7 hop limit was imposed along
with a requirement that each bridge should forward
each frame within one second (or drop it) as part of the
STP timing budget.

Today these numbers seem somewhat laughable
(1Gbps for 1 sec would require a 100M Byte buffer)
however as far as I know (you should check for yourself
since I have not read 802.1d for years) the standard
has never been changed in this respect.

There seems to me no reason not to increase the
number of bridge hops used if STP is not
involved.

A couple of things to ponder.

Support - If you tell your support channel that you are
not compliant with the standard then I strongly suspect
that they will be reluctant to assist.

Probability of packet loss - If you do not recover from
lost data then you should carefuly consider the
increased probability of lost packets.

Maintainability - I do not know what you do at present
however if you were to use low cost switches that
cannot report or record errors or problems
it will be very difficult to troubleshoot network
failures.

Good luck.



NMFall 20%
Posted by Al Dykes on October 31, 2005, 11:51 am
If you were  Registered and logged in, you could reply and use other advanced thread options


>1. Eddie Oct 28, 8:30 pm show options
>
>Newsgroups: comp.dcom.lans.ethernet
>Date: 28 Oct 2005 13:30:35 -0700
>Local: Fri, Oct 28 2005 8:30 pm
>Subject: ethernet point to point wiring
>Reply | Reply to Author | Forward | Print | Individual Message | Show
>original | Report Abuse
>
>> I am looking to replace an old serial RS485 multidrop point to point
>> communications line with ethernet but would like to retain the wiring
>> savings in a point to point layout. On RS485 we can connect 32 devices
>> with series point to point wiring. I have done some research that
>> indicates that if I used a switch at each device I would be limited to
>> a maximum of 7. Is this correct, or are new switches able to exceed
>> that number? If so, how many can I realistically connect in a point to
>> point topology.
>
>Is I understand it the 7 hop limit was imposed along
>with a requirement that each bridge should forward
>each frame within one second (or drop it) as part of the
>STP timing budget.
>
>Today these numbers seem somewhat laughable
>(1Gbps for 1 sec would require a 100M Byte buffer)
>however as far as I know (you should check for yourself
>since I have not read 802.1d for years) the standard
>has never been changed in this respect.
>
>There seems to me no reason not to increase the
>number of bridge hops used if STP is not
>involved.
>
>A couple of things to ponder.
>
>Support - If you tell your support channel that you are
>not compliant with the standard then I strongly suspect
>that they will be reluctant to assist.
>
>Probability of packet loss - If you do not recover from
>lost data then you should carefuly consider the
>increased probability of lost packets.
>
>Maintainability - I do not know what you do at present
>however if you were to use low cost switches that
>cannot report or record errors or problems
>it will be very difficult to troubleshoot network
>failures.
>


You didn't say how many stations you want to wire but if it's a small
number, pull wire and do it right. It won't cost much.

If you are doing it for a large operation then do it right or you'll
spend your days under desks and with unhappy users and then your
successor will rewire the place, correctly.





--
a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.


Posted by Eddie on October 31, 2005, 10:32 am
If you were  Registered and logged in, you could reply and use other advanced thread options


Thanks to all for your comments. It appears that this solution won't
do for our application. Our typical installation would involve 10-30
controllers on a single RS485 multi-drop cable in the 1000+ft total
length range. With this layout and our polling master/slave protocol,
Modbus/RTU serial at 19.2kbaud, we typically get 1-2
updates/second/controller if requesting several bytes of data from each
controller. The Modbus/RTU serial protocol is only typically supported
at speeds up to 38.4kbaud, so a simple baud rate increase isn't a
soultion. A fairly seamless change for us would be to put all of these
controllers onto ethernet running Modbus/TCP protocol which wraps the
same serial command string into a TCP packet and uses ethernet for
transport. The major issue for our isnstallations with ethernet is the
home run wiring costs. Most of our wiring installations require
electrical conduit with a final installed cost of ~$10/ft which is much
larger than the cost of the cable itself. Therefore, anything we can
do to decrease the total installed feet of cable/conduit is a big cost
saver to our end users.

It sounds to me like the best solution for us if we want to utilize
ethernet is to put some centrally located multiple port switches in the
field and link them together to give the most effiecient layout.

Thanks again for your comments.

Ed



Posted by James Knott on November 1, 2005, 9:05 pm
If you were  Registered and logged in, you could reply and use other advanced thread options


anybody43@hotmail.com wrote:

>> I am looking to replace an old serial RS485 multidrop point to point
>> communications line with ethernet but would like to retain the wiring

When you reply to my messages, please quote something I actually said,
instead of making it appear as though I said something I didn't.


Similar ThreadsPosted
MAC addresses in router vs Access Point May 1, 2008, 5:19 am
Windows PC As IEEE 802.11 Access Point June 25, 2008, 4:43 pm
Difference between bridge and wireless access point?? October 9, 2007, 6:57 pm
May I use a Linksys WRT54G router as secondary wireless access point? January 25, 2006, 10:28 pm
move a ethernet wiring closet January 15, 2007, 8:23 pm
really bad wiring jobs April 21, 2007, 5:53 am
What's the going rate for LAN wiring? March 5, 2008, 12:37 am
Problem with wiring a networking device or devices May 14, 2005, 10:04 pm
USB Ethernet controllers that use the ASIX AX88772 or AX88172 USB-Ethernet bridge devices August 19, 2005, 4:04 pm
Difference between Ethernet 2 and 802.3 Frame per the Ethernet FAQ July 28, 2006, 9:02 am

other useful resources:
The Federal Communications Commission (FCC)
Telecommunications Industry Association
Electronic and Software Security Products and Services
International Telecommunication Union

Custom CGI Perl and PHP programming by 1-Script.com

Contact Us | Privacy Policy
The site map in XML format XML site map